.\"
.\" Copyright (c) 2019 Ian Lepore <ian@freebsd.org>
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\"
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
.Dd June 24, 2025
.Dt ELF_AUX_INFO 3
.Os
.Sh NAME
.Nm elf_aux_info
.Nd extract data from the elf auxiliary vector of the current process
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sys/auxv.h
.Ft int
.Fn elf_aux_info "int aux" "void *buf" "int buflen"
.Sh DESCRIPTION
The
.Fn elf_aux_info
function retrieves the auxiliary info vector requested in
.Va aux .
The information is stored into the provided buffer if it will fit.
The following values, defined in
.In sys/elf_common.h
can be requested (corresponding buffer sizes are specified in parenthesis):
.Bl -tag -width AT_OSRELDATE
.It AT_CANARY
The canary value for SSP (arbitrary sized buffer, as many bytes are
returned as it fits into it, rest is zeroed).
.It AT_EXECPATH
The path of executed program
.Dv (MAXPATHLEN).
This may not be present if the process was initialized by
.Xr fexecve 2
and the namecache no longer contains the file's name.
.It AT_HWCAP
CPU / hardware feature flags
.Dv (sizeof(u_long)).
.It AT_HWCAP2
CPU / hardware feature flags
.Dv (sizeof(u_long)).
.It AT_HWCAP3
CPU / hardware feature flags
.Dv (sizeof(u_long)).
.It AT_HWCAP4
CPU / hardware feature flags
.Dv (sizeof(u_long)).
.It AT_NCPUS
Number of CPUs
.Dv (sizeof(int)).
.It AT_OSRELDATE
The
.Dv OSRELDATE
of the kernel or jail the program is running on
.Dv (sizeof(int)).
.It AT_PAGESIZES
Vector of page sizes (arbitrary sized buffer, as many elements of the
.Dv pagesizes
array are returned as it fits).
.It AT_PAGESZ
Page size in bytes
.Dv (sizeof(int)).
.It AT_TIMEKEEP
Pointer to VDSO timehands (for library internal use,
.Dv sizeof(void *)).
.It AT_USRSTACKBASE
Top of the user stack for main thread.
.It AT_USRSTACKLIM
Limit for grow of the user stack for main thread.
.El
.Sh RETURN VALUES
Returns zero on success, or an error number on failure.
.Sh ERRORS
.Bl -tag -width Er
.It Bq Er EINVAL
An unknown item was requested.
.It Bq Er EINVAL
The provided buffer was not the right size for the requested item.
.It Bq Er ENOENT
The requested item is not available.
.El
.Sh HISTORY
The
.Fn elf_aux_info
function appeared in
.Fx 12.0 .
.Sh BUGS
Only a small subset of available auxiliary info vector items are
accessible with this function.
Some items require a "right-sized" buffer while others just require a
"big enough" buffer.
